Plasma processing and plasma processing apparatuses have become indispensable in the manufacturing of ultra-fine semiconductor devices which are called recently deep submicron devices or deep sub-quarter micron devices, having a gate length of 0.1 μm or less, or in the manufacturing of high resolution flat panel display devices including liquid crystal display devices.
Various plasma exciting methods are conventionally used for plasma processing apparatuses used to manufacture semiconductor devices or liquid crystal display devices. In particular, parallel-plate type high frequency excitation plasma processing apparatuses or induction-coupled type plasma processing apparatuses are generally used as plasma processing apparatuses. However, these conventional plasma processing apparatuses have a drawback in that since the formation of plasma is not uniform and regions of high electron density are limited, it is difficult for conventional plasma processing apparatuses to achieve uniform processing over the entire surface of a substrate to be processed at a high processing speed, that is, at a high throughput. This problem becomes particularly serious when a substrate having a large diameter is processed. Further, these conventional plasma processing apparatuses suffer from some inherent problems, such as damage to the semiconductor devices formed on the substrate to be processed due to their high electron temperature, and, severe metal contamination caused by sputtering of a processing chamber wall. Thus, it is becoming more difficult for conventional plasma processing apparatuses to satisfy the constant demand for further miniaturization of semiconductor devices or liquid crystal display devices and further improvement in productivity.
To solve this difficulty, a conventional microwave plasma processing apparatus that uses high-density plasma excited by a microwave electric field without using a direct current magnetic field has been proposed. For example, a plasma processing apparatus, having a construction in which microwaves are radiated to a processing chamber from a planar antenna (radial-line slot antenna) having a number of slots arranged to radiate uniform microwaves, the gas inside the processing chamber is ionized by the microwave electric field to generate plasma, has been proposed (for example, refer to Japanese Laid-Open Patent Publication No. Hei 9-63793 (hereinafter, referred to as Reference 1)). In the plasma excited by the microwave electric field, it is possible to realize a high plasma density over a wide area below the planar antenna, and it is possible to conduct uniform plasma processing in a short time. Further, since the electron temperature is low in the plasma formed by the microwave electric field, it is possible to avoid damage being caused to or metal contamination of the substrate to be processed. Further, since it is possible to excite uniform plasma over a large area of a substrate, the above-mentioned technology can be easily applied to the manufacturing process of semiconductor devices by using semiconductor substrates having large diameters or manufacturing of large liquid crystal display devices.
Plasma processing apparatuses use a shower plate including a plurality of vertical holes as gas release holes in order to uniformly supply a gas for exciting plasma into a processing chamber. However, when using the shower plate, plasma formed right below the shower plate may flow backwards through the vertical holes of the shower plate, which causes an abnormal discharge or deposition of gases, and thus transmission efficiency of microwaves for plasma excitation or yield of devices deteriorates.
Many structures of the shower plate have been suggested to prevent the reverse flow of plasma through the vertical holes.
For example, in Japanese Laid-Open Patent Publication No. 2005-33167 (hereinafter, referred to as Reference 2), the hole diameter of a gas release hole formed in the leading end of a vertical hole of a shower plate is set to not greater than twice the sheath thickness of plasma formed right below the shower plate. However, it is insufficient to reduce the hole diameter of the gas release hole in order to prevent the reverse flow of plasma. In particular, if a plasma density is increased from 1012 cm−3, which is a conventional value, to 1013 cm−3 in order to reduce damage and increase a processing speed, it is impossible to prevent the reverse flow of plasma by only controlling the hole diameter of the gas release hole since the reverse flow of plasma increases. Also, it is difficult to form the gas release hole having a micro hole diameter by processing a hole of a shower plate body, and is problematic in terms of processability.
Japanese Laid-Open Patent Publication No. 2004-39972 (hereinafter, referred to as Reference 3) discloses the use of a shower plate that is a porous ceramic sintered body having gas permeability. The shower plate is for preventing the reverse flow of plasma by the walls of a plurality of pores included in the porous ceramic sintered body.
However, the shower plate having general porous ceramic sintered body sintered at a normal temperature and a pressure is not good in surface planarization since the shower plate includes pores having a large deviation between several μm and several tens of μm in terms of pore diameters, has a large maximum crystal diameter of 20 μm, and does not have a uniform structure. If a surface of the shower plate being exposed to plasma is the porous ceramic sintered body, an effective surface area increases, and electron and ion recombination of the plasma increases, which deteriorate power efficiency of excitation of plasma. In this regard, the Reference 3 discloses, instead of wholly forming the shower plate as the porous ceramic sintered body, forming a structure of the shower plate formed of dense alumina in which an opening for releasing gas is formed, and the general porous ceramic sintered body sintered at the normal temperature and pressure is fitted into the opening, and then gas is released through the porous ceramic sintered body. However, since the structure uses the porous ceramic sintered body sintered at the ordinary temperature and pressure, the above-mentioned problem caused by poor surface-planarization has not been solved.
Also, in International Publication WO06/112392 (hereinafter, referred to as Reference 4), the applicant of the present application has suggested preventing the reverse flow of plasma by not adjusting the structure of a shower plate but adjusting a diameter size of a gas release hole. In more detail, the diameter size of the gas release hole is set less than 0.1˜0.3 mm, and a tolerance accuracy of the diameter size is set to within ±0.002 mm, and thus the reverse flow of plasma is prevented and no variation in the amount of released gas occurs.
However, when the shower plate has been actually used for a microwave plasma processing apparatus under plasma density conditions of 10−3 cm−3, as shown in FIG. 10, a discolored light brown portion is seen as a result of the reverse flow of plasma into a space 402 for charging plasma excitation gas formed between a shower plate body 400 and a cover plate 401 and a vertical hole 403 in communication with the space 402.
To address the above-mentioned problems, in Japanese Patent Application Nos. 2006-163357, 2006-198762, and 2006-198754 (hereinafter, referred to as References 5 through 7, respectively), the applicant of the present application has suggested fitting a ceramic member having a plurality of gas release holes or a porous gas-communicating body having pores communicating in a gas-communicating direction into a vertical hole of a shower plate as a release path for plasma excitation gas.
In the References 5 through 7, the shower plate can prevent the reverse flow of plasma even under plasma density conditions of 1013 cm−3.
However, since the shower plate has been repeatedly used for a microwave plasma processing apparatus, the ceramic member or the porous gas-communicating body fitted into the vertical hole of the shower plate partially or wholly comes out from the vertical hole of the shower plate. This is a result of a reduction in the adherence between the ceramic body or the porous gas-communicating body and the vertical hole of the shower plate, caused by thermal stress or thermal deformation that occurs when using the shower plate.